Terminal velocity of bombs?

Walt BJ wrote:
There's a Tall Boy at at the USAF museume at Dayton. There's a 44,000
pound T12 standing door guard at the Aberdeen Proving Ground Museum
building. ISTR both have canted fins. (I trust both are inert shapes.)
Quite a few 'drop models' of weighted models of proposed aircraft went
supersonic when released at high altitude. Telemetry relayed what
happened on the way down. ISTR the Miles M52 was tested this way.
FWIW Mk 82 slicks separate just fine and hit the target accurately
when released supersonic - (G).
Walt BJ

http://www.johnmullen.org.uk/aerospce/pics/bombs.htm

The bomb was always intended to have a backspin, as that would enable it to
bounce over the torpedo nets. When it hit the wall of the dam, the spin
would ensure that it remained there as it sank to it's detonation depth,
rather than bounce away from it.

Wallis intended that the bomb would be a sphere, but a cylinder was the
easiest shape to manufacture out of sheet metal. To maintain the spherical
shape, they initally surrounded the cylinder with a wooden sphere, but this
disintergrated the instant the first test bomb hit the water. No matter ...
the cylinder bounced just as well!

"John Halliwell" wrote in message
news
In article ,
BackToNormal writes
Phew John. I opened a can of worms here by mentioning the program I saw.
It said the bomb was designed to hit the dam wall, bounce away, and then
the gyroscopic motion would claw the bomb back to and down against the
wall to detonate at predetermined depth.

It's hard to be sure exactly what led to what (cause & effect) of the
various techniques used in designing the bomb. My understanding (mostly
gained from Brickhill), is that originally Barnes used a sphere to
ensure each bounce would present the same surface to the water. He found
it would be too big and stretched it to a cylinder, adding spin to
stabilise it. Not sure if he tried forward spin or not, but he found
back spin allowed it to 'skip' off the water. The crawling down the dam
wall was discovered during testing as an additional benefit.

Highball, the smaller anti-shipping version which didn't go into
service, was pretty much spherical (only the very ends were flat to
allow it to be attached to the spinning gear).

It sounds like there are different accounts, and the whole thing was
probably muddied by wartime secrecy (the 1954 film was not allowed to
mention anything of the back-spin as that was still secret). It is also
possible that later editions of The Dam Busters might have more
information as more was released.

The spin was primarily designed to work the same as spin put on a golf
ball to keep the bomb against the wall, and not as a trajectory aid.
No?

Different accounts suggest different developments, but at the end of the
day, they're all correct when it comes to the operation of the bomb.
There is also the possibility of each account being tailored to a given
audience or compiled to fit the 'established history'. Brickhill's
account is probably incomplete or inaccurate in many ways.

A good, more recent account is given in 'The Dambusters Raid', one of
the 'Cassell Military Paperbacks' series (sorry haven't got more details
to hand). It clears up a number of points and tries to identify where
many of the 'missing' aircraft were shot down.

Just out of interest, what was the angle Nat Geo used in the programme,
seems a bit out of character (I only read the magazine, haven't seen any
of their TV progs)?

--
John

John Halliwell wrote:

In article ,
BackToNormal writes

Phew John. I opened a can of worms here by mentioning the program I saw.
It said the bomb was designed to hit the dam wall, bounce away, and then
the gyroscopic motion would claw the bomb back to and down against the
wall to detonate at predetermined depth.

It's hard to be sure exactly what led to what (cause & effect) of the
various techniques used in designing the bomb. My understanding (mostly
gained from Brickhill), is that originally Barnes used a sphere to
ensure each bounce would present the same surface to the water. He found
it would be too big and stretched it to a cylinder, adding spin to
stabilise it. Not sure if he tried forward spin or not, but he found
back spin allowed it to 'skip' off the water. The crawling down the dam
wall was discovered during testing as an additional benefit.

Highball, the smaller anti-shipping version which didn't go into
service, was pretty much spherical (only the very ends were flat to
allow it to be attached to the spinning gear).

It sounds like there are different accounts, and the whole thing was
probably muddied by wartime secrecy (the 1954 film was not allowed to
mention anything of the back-spin as that was still secret). It is also
possible that later editions of The Dam Busters might have more
information as more was released.

The spin was primarily designed to work the same as spin put on a golf
ball to keep the bomb against the wall, and not as a trajectory aid.
No?

Different accounts suggest different developments, but at the end of the
day, they're all correct when it comes to the operation of the bomb.
There is also the possibility of each account being tailored to a given
audience or compiled to fit the 'established history'. Brickhill's
account is probably incomplete or inaccurate in many ways.

A good, more recent account is given in 'The Dambusters Raid', one of
the 'Cassell Military Paperbacks' series (sorry haven't got more details
to hand). It clears up a number of points and tries to identify where
many of the 'missing' aircraft were shot down.

Just out of interest, what was the angle Nat Geo used in the programme,
seems a bit out of character (I only read the magazine, haven't seen any
of their TV progs)?

I've had another look at the bit of the Nat Geo program I managed to
tape.

They do say the spin was put on the bomb to make it claw its way back to
the dam wall (after its initial bounce off) and there were animations to
demonstrate this. There was no mention of spin helping to control bounce
or direction. Some of the original footage showed one of the bombs
hitting and going from backspin, to sideways, to forwards spin. Their
hair must have turned white while they were experimenting.

Regarding backspin, I'd have thought forward gyroscopic spin would have
worked better against the dam wall (which probably explains why I am not
a scientist).

After the prog finished, my wife (avid low handicap golfer) commented
that she was unaware that golf balls have dimples as a result of
Wallis' experiments with dimples on his spherical bombs. Actually, I
thought the program suggested that too, but golf balls had dimples a
long time before Wallis did his thing. Maybe we both misinterpreted the
program.

ronh
--
"People do not make decisions on facts, rather,
how they feel about the facts" Robert Consedine